Unveiling the Layers: Delving into the Sitecore Tech Stack: Avoiding React Hydration Warnings When Rendering Sitecore Dynamic Placeholders

If you’re working with React and Next.js — especially with Sitecore JSS — you might have run into a confusing warning like this:

“This Suspense boundary received an update before it finished hydrating.”

It sounds scary, but it basically means React got confused while it was trying to “wake up” the server-rendered HTML and make it interactive on the browser.

In this post, I’ll explain what hydration means, why this error happens, and how I fixed it when rendering Sitecore placeholders inside a React component.

What is Hydration?

When you use Next.js, React first renders your page on the server and sends the HTML to the browser. This lets your users see the page quickly, which is great for speed and SEO.

But the HTML alone isn’t interactive — buttons won’t work, forms won’t submit, and React logic isn’t running yet.

That’s where hydration comes in. Hydration is React’s process of attaching event handlers and React’s internal state to the existing HTML in the browser. It “wakes up” the static content and makes it dynamic.

Why Do Hydration Errors Happen?

React expects the HTML it rendered on the server and the HTML it’s trying to “hydrate” on the client to match exactly.

If something changes the HTML too early — like React updating state or an external library injecting components before hydration finishes — React gets confused. That’s when you see errors like:

“This Suspense boundary received an update before it finished hydrating.”

The Problem with Sitecore Placeholders

Sitecore JSS uses placeholders where it dynamically injects components inside your React app.

The problem is, these placeholders might get filled with content before React finishes hydrating. This causes React to detect that the DOM changed unexpectedly during hydration — triggering the error.

How I Fixed It — Waiting for Hydration Before Rendering Placeholders

The fix is pretty simple:

I added a React state variable called hydrated that starts as false.
I used useEffect to set hydrated to true after hydration completes.
I only render the Sitecore placeholders when hydrated is true.

Here’s the key part of the code:

Why Does This Work?

On the server, hydrated is false, so placeholders aren’t rendered. This keeps the server HTML simple and stable.
On the client, React hydrates the static HTML first (no placeholders yet).
After hydration, useEffect runs and sets hydrated to true, triggering a re-render that includes placeholders.
Since placeholders render after hydration, React doesn’t get confused and the error goes away.

Final Thoughts

Hydration errors can be tricky, but they come down to React needing the server HTML and client React tree to match exactly during hydration.

By waiting until hydration finishes before rendering dynamic parts like Sitecore placeholders, you can avoid those warnings and keep your app stable and fast.

If you’re working with Next.js and Sitecore JSS, I hope this simple fix helps you out!